The fuel system pressurizes the fuel pump to prevent it from over pressurizing and making the car go boom. Remember that venting regulates the pressure in the fuel tank since the temperatures will cause the fuel to expand leading to increased pressure inside. Not having a vent may lead to an increase in the pressure, which in turn can lead to problems with fuel delivery, decreased efficiency, or in worst case, destroy one of the components of the fuel system. Venting is critical though — a fuel tank will be under over 10 psi on a hot day without it, and this isnld8217;t good for the fuel pump.
Venting is also a key component of evaporative emissions, which is regulated in many countries. It operates by capturing and directing the unhealthy fuel vapors that would otherwise escape into the atmosphere through a charcoal canister and into the air. According to the Environmental Protection Agency (EPA), this emissions technology in newer vehicles cuts hydrocarbons by about 80%. This is a design with environmental code of conduct and gives a performance boost to car by maintaining constant fuel pressure for better combustion.
When things heat up and fuel demand is extreme, especially in motorsports, a vented fuel system is a must. For racing companies such as NASCAR, they also shoot for constant fuel flow under extreme conditions by utilizing vented fuel pumps, which prevent vapor lock (a state of vaporizing liquid fuel, which prevents flow). Which leads to the words of performance engineer Gale Banks, who said, “In high-performance applications, far too many times have I seen a sealed fuel system be the difference between a podium and a DNF (Did Not Finish).”
This venting system also lowers the potential for fuel vapor accumulation that could affect fuel pump longevity and performance. For example, the fuel pump would have to work harder to pull fuel from a pressure-bound tank — which would shorten the pump’s life considerably without venting. Instead, modern vehicles generally employ complex pressure sensors and control modules that monitor the saturation of the evaporative emissions system, and actively adjust venting or enhancement based on the fuel tank pressure to maintain a safe and balanced state.
This Fuel Pump resource has a lot more information about venting and how to keep the system working properly.